1. Field of the Invention
The present invention relates to a communication apparatus and to a method of controlling the same.
2. Description of the Related Art
The HDMI 1.4 specification provides for an additional high-speed communication channel (HEAC: HDMI Ethernet and Audio Return Channel) for implementing an Ethernet (registered trademark) communication channel (HEC: HDMI Ethernet Channel) and an audio return channel (ARC: Audio Return Channel). With regard to cable specifications as well, this has been accompanied by the addition of CAT-1 wHEAC and CAT-2 wHEAC, which make possible high-speed communication equivalent to 100 Base-Tx, to the conventional CAT-1/CAT-2. Since the cables conforming to these four types of specifications are all identical in shape, their specifications cannot be distinguished visually.
Further, according to the HDMI 1.4 specification, a source device and a sink device are capable of verifying each other's device capabilities (HEAC function operative/inoperative) by CDC communication via a CEC line. A method of sensing the HDMI cable specification, however, has not been defined.
For this reason, even if a source device and a sink device have been connected by a “poor-quality cable” or “HEAC non-compliant cable”, this cannot be sensed. In such case, even if the source device and sink device comply with HEAC, there is a possibility that HEC communication will become unstable or impossible owing to attenuation of the HEAC signal on the transmission line.
A method of transmitting a signal upon first amplifying it beforehand by the amount of signal attenuation has been proposed as a measure to deal with signal attenuation on a transmission line (see the specification of Japanese Patent Laid-Open No. 6-37675).
However, signals of multiple types (an HEC signal and ARC signal) are superimposed upon an HEAC signal. As a consequence, when the above-mentioned technique is applied to HEAC communication to amplify the HEAC signal, there is a possibility that even if one of the HEC and ARC signals is amplified suitably, the other signal will be amplified excessively and communication failure will occur. For example, in a case where the amplification factor is decided and the HEAC signal amplified in such a manner that stable HEC communication becomes possible, HEC communication will become possible by amplifying the HEC signal to the appropriate level. However, there is a possibility that the ARC signal will be amplified excessively.